A multifunctional system for genome editing and large-scale interspecies gene transfer

Bioremediation of complex organic pollutants by engineered Vibrio natriegens

Industrial wastewater, petroleum pollution and plastic contamination are significant threats to global marine biosecurity because of their toxic, mutagenic and persistent nature1. The use of microorganisms in bioremediation has been constrained by the complexity of organic pollutants and limited tolerance to saline stress2. In this study, we used synthetic biology to engineer Vibrio natriegens into a strain capable of bioremediating complex organic pollutants in saline wastewater and soils. The competence master regulator gene tfoX was inserted into chromosome 1 of the V. natriegens strain Vmax and overexpressed to enhance DNA uptake and integration. Degradation gene clusters were chemically synthesized and assembled in yeast. We developed a genome engineering method (iterative natural transformation based on Vmax with amplified tfoX effect) to transfer five gene clusters (43 kb total) into Vmax. The engineered strain has the ability to bioremediate five organic pollutants (biphenyl, phenol, naphthalene, dibenzofuran and toluene) covering a broad substrate range, from monocyclic to multicyclic compounds, in industrial wastewater samples from a chlor-alkali plant and a petroleum refinery.

Integrase enables synthetic intercellular logic via bacterial conjugation

Integrases have been widely used in synthetic biology for genome engineering and genetic circuit design. They mediate DNA recombination to alter the genotypes of single cell lines in vivo, with these changes being permanently recorded and inherited via vertical gene transfer. However, integrase-based intercellular DNA messaging and its regulation via horizontal gene transfer remain underexplored. Here, we introduce a versatile strategy to design, build, and test integrase-based intercellular DNA messaging through bacterial conjugation. First, we screened conjugative plasmids and recipient cells for efficient conjugation. Then, we established a layered framework to describe the interactions among hierarchical E. coli strains and implemented dual-layer Boolean logic gates to demonstrate intercellular DNA messaging and management. Finally, we expanded the design to include four-layer single-processing pathways and dual-layer multi-processing systems. This strategy advances intercellular DNA messaging, hierarchical signal processing, and the application of integrase in systems and synthetic biology.

Antibiotics-Free Steady Bioproduction of Valuable Chemicals from Organic Wastes by Engineered Vibrio natriegens through Targeted Gene Integration

Bioproduction of chemicals by using engineered bacteria is promising for a circular economy but challenged the instability of the introduced plasmid by conventional methods. Here, we developed a two-plasmid INTEGRET system to reliably integrate the targeted gene into the Vibrio natriegens genome, making it a powerful strain for efficient and steady bioproduction without requiring antibiotic addition. The INTEGRET system allows for gene insertion at over 75% inserting efficiency and flexibly controllable gene dosages. Additionally, simultaneous gene insertion at four genomic sites was achieved at 54.3% success rate while maintaining stable inheritance of exogenous sequences across multiple generations. The engineered strain could efficiently synthesize PHB from the fermentation of diverse organic wastes, with an efficiency comparable to those with overexpressed plasmid. When the mixture of seawater and molasses was used as the feedstock, it achieved a high PHB yield of 39.41 wt %. An extended application of the INTEGRET system for imparting the riboflavin production ability to the bacterium was also demonstrated. Our work presents a reliable and efficient genomic editing tool to facilitate the development of sustainable and environmentally benign biological platforms for converting biomass wastes into valuable chemicals.

The new chassis in the flask: Advances in Vibrio natriegens biotechnology research

Biotechnology has been built on the foundation of a small handful of well characterized and well-engineered organisms. Recent years have seen a breakout performer gain attention as a new entrant into the bioengineering toolbox: Vibrio natriegens. This review covers recent research efforts into making V. natriegens a biotechnology platform, using a large language model (LLM) and knowledge graph to expedite the literature survey process. Scientists have made advancements in research pertaining to the fundamental metabolic characteristics of V. natriegens, development and characterization of synthetic biology tools, systems biology analysis and metabolic modeling, bioproduction and metabolic engineering, and microbial ecology. Each of these subcategories has relevance to the future of V. natriegens for bioengineering applications. In this review, we cover these recent advancements and offer context for the impact they may have on the field, highlighting benefits and drawbacks of using this organism. From examining the recent bioengineering research, it appears that V. natriegens is on the precipice of becoming a platform bacterium for the future of biotechnology.

Vibrio natriegens: Application of a Fast-Growing Halophilic Bacterium

The fast growth accompanied with high substrate consumption rates and a versatile metabolism paved the way to exploit Vibrio natriegens as unconventional host for biotechnological applications. Meanwhile, a wealth of knowledge on the physiology, the metabolism, and the regulation in this halophilic marine bacterium has been gathered. Sophisticated genetic engineering tools and metabolic models are available and have been applied to engineer production strains and first chassis variants of V. natriegens. In this review, we update the current knowledge on the physiology and the progress in the development of synthetic biology tools and provide an overview of recent advances in metabolic engineering of this promising host. We further discuss future challenges to enhance the application range of V. natriegens.

CRISPR-Cas9-assisted genome editing in E. coli elevates the frequency of unintended mutations

Cas-assisted lambda Red recombineering techniques have rapidly become a mainstay of bacterial genome editing. Such techniques have been used to construct both individual mutants and massive libraries to assess the effects of genomic changes. We have found that a commonly used Cas9-assisted editing method results in unintended mutations elsewhere in the genome in 26% of edited clones. The unintended mutations are frequently found over 200 kb from the intended edit site and even over 10 kb from potential off-target sites. We attribute the high frequency of unintended mutations to error-prone polymerases expressed in response to dsDNA breaks introduced at the edit site. Most unintended mutations occur in regulatory or coding regions and thus may have phenotypic effects. Our findings highlight the risks associated with genome editing techniques involving dsDNA breaks in E. coli and likely other bacteria and emphasize the importance of sequencing the genomes of edited cells to ensure the absence of unintended mutations.

Investigation of exopolysaccharide formation and its impact on anaerobic succinate production with Vibrio natriegens

Vibrio natriegens is an emerging host for biotechnology due to its high growth and substrate consumption rates. In industrial processes typically fed-batch processes are applied to obtain high space-time yields. In this study, we established an aerobic glucose-limited fed-batch fermentation with the wild type (wt) of V. natriegens which yielded biomass concentrations of up to 28.4 gX  L-1 . However, we observed that the viscosity of the culture broth increased by a factor of 800 at the end of the cultivation due to the formation of 157 ± 20 mg exopolysaccharides (EPS) L-1 . Analysis of the genomic repertoire revealed several genes and gene clusters associated with EPS formation. Deletion of the transcriptional regulator cpsR in V. natriegens wt did not reduce EPS formation, however, it resulted in a constantly low viscosity of the culture broth and altered the carbohydrate content of the EPS. A mutant lacking the cps cluster secreted two-fold less EPS compared to the wt accompanied by an overall low viscosity and a changed EPS composition. When we cultivated the succinate producer V. natriegens Δlldh Δdldh Δpfl Δald Δdns::pycCg (Succ1) under anaerobic conditions on glucose, we also observed an increased viscosity at the end of the cultivation. Deletion of cpsR and the cps cluster in V. natriegens Succ1 reduced the viscosity five- to six-fold which remained at the same level observed at the start of the cultivation. V. natriegens Succ1 ΔcpsR and V. natriegens Succ1 Δcps achieved final succinate concentrations of 51 and 46 g L-1 with a volumetric productivity of 8.5 and 7.7 gSuc L-1  h-1 , respectively. Both strains showed a product yield of about 1.4 molSuc molGlc -1 , which is 27% higher compared with that of V. natriegens Succ1 and corresponds to 81% of the theoretical maximum.

Ploidy in Vibrio natriegens: Very Dynamic and Rapidly Changing Copy Numbers of Both Chromosomes

Vibrio natriegens is the fastest-growing bacterium, with a doubling time of approximately 12-14 min. It has a high potential for basic research and biotechnological applications, e.g., it can be used for the cell-free production of (labeled) heterologous proteins, for synthetic biological applications, and for the production of various compounds. However, the ploidy level in V. natriegens remains unknown. At nine time points throughout the growth curve, we analyzed the numbers of origins and termini of both chromosomes with qPCR and the relative abundances of all genomic sites with marker frequency analyses. During the lag phase until early exponential growth, the origin copy number and origin/terminus ratio of chromosome 1 increased severalfold, but the increase was lower for chromosome 2. This increase was paralleled by an increase in cell volume. During the exponential phase, the origin/terminus ratio and cell volume decreased again. This highly dynamic and fast regulation has not yet been described for any other species. In this study, the gene dosage increase in origin-adjacent genes during the lag phase is discussed together with the nonrandom distribution of genes on the chromosomes of V. natriegens. Taken together, the results of this study provide the first comprehensive overview of the chromosome dynamics in V. natriegens and will guide the optimization of molecular biological characterization and biotechnological applications.

CRISPR/FnCas12a-mediated efficient multiplex and iterative genome editing in bacterial plant pathogens without donor DNA templates

CRISPR-based genome editing technology is revolutionizing prokaryotic research, but it has been rarely studied in bacterial plant pathogens. Here, we have developed a targeted genome editing method with no requirement of donor templates for convenient and efficient gene knockout in Xanthomonas oryzae pv. oryzae (Xoo), one of the most important bacterial pathogens on rice, by employing the heterologous CRISPR/Cas12a from Francisella novicida and NHEJ proteins from Mycobacterium tuberculosis. FnCas12a nuclease generated both small and large DNA deletions at the target sites as well as it enabled multiplex genome editing, gene cluster deletion, and plasmid curing in the Xoo PXO99A strain. Accordingly, a non-TAL effector-free polymutant strain PXO99AD25E, which lacks all 25 xop genes involved in Xoo pathogenesis, has been engineered through iterative genome editing. Whole-genome sequencing analysis indicated that FnCas12a did not have a noticeable off-target effect. In addition, we revealed that these strategies are also suitable for targeted genome editing in another bacterial plant pathogen Pseudomonas syringae pv. tomato (Pst). We believe that our bacterial genome editing method will greatly expand the CRISPR study on microorganisms and advance our understanding of the physiology and pathogenesis of Xoo.

The role of replication-induced chromosomal copy numbers in spatio-temporal gene regulation and evolutionary chromosome plasticity

For a coherent response to environmental changes, bacterial evolution has formed a complex transcriptional regulatory system comprising classical DNA binding proteins sigma factors and modulation of DNA topology. In this study, we investigate replication-induced gene copy numbers - a regulatory concept that is unlike the others not based on modulation of promoter activity but on replication dynamics. We show that a large fraction of genes are predominantly affected by transient copy numbers and identify cellular functions and central pathways governed by this mechanism in Escherichia coli. Furthermore, we show quantitatively that the previously observed spatio-temporal expression pattern between different growth phases mainly emerges from transient chromosomal copy numbers. We extend the analysis to the plant pathogen Dickeya dadantii and the biotechnologically relevant organism Vibrio natriegens. The analysis reveals a connection between growth phase dependent gene expression and evolutionary gene migration in these species. A further extension to the bacterial kingdom indicates that chromosome evolution is governed by growth rate related transient copy numbers.